The Doebner-Miller reaction (Doebner et al., Ber., 14, 2816 (1881) has been used for the preparation of substituted quinaldines for over 100 years. However, low yields and purification problems have led to many investigations of improved syntheses. Among these are: Utermohlen, J. Org. Chem., 8, 544 (1943); Spivey et al, J. Chem. Soc., 2656 (1949); and Leir, J. Org. Chem., 42, 911 (1977).
U.S. Pat. No. 4,851,409 teaches the preparation of substituted quinaldines using ZnCl.sub.2 to precipitate the end product, as described by Leir. U.S. Pat. No. 4,851,409 is incorporated herein by reference for its teaching of the use of 7-chloroquinaldine as a starting material for the preparation of 2-substituted quinoline dioic acids which are antagonists of leukotriene and useful as anti-asthma drugs.